Internal combustion engines that propel motor vehicles are typically electrically started by turning an ignition switch to a start position that causes the engine to be cranked by an electric starter motor. When the engine has started, the switch is released from start position to assume a run position. In start position, electric current flows from a bank of one or more D.C. storage batteries to the electric starter motor that cranks the engine through a set of gears. The amount of current is typically very large, and consequently, heavy electrical cable is typically employed to conduct the current without the presence of any circuit protection device to protect against a short in the cable or the starter motor.
When the cable is routed in a vehicle, attention must be given to the routing path and how the cable is secured to minimize the possibility of a short. Moreover, if a short were to occur in the starter motor itself, even careful routing of the cable would be of no avail.
When the engine is running, an engine-driven alternator generates current for keeping the battery bank charged. To provide some degree of protection against a short, a fusible link may be present in the charging circuit between the alternator and the battery bank. While a fusible link provides some protection against a short between the alternator and battery bank, it does so at the expense of creating additional resistance in the charging circuit from the alternator to the battery. The voltage drop across the fusible link generates wasteful heat and over time may result in less than optimum battery charging that can lead eventually to a weakened battery, a condition that is not desirable, especially in cold weather.
One general aspect of the invention relates to a motor vehicle comprising an engine that is started by cranking and an electrical system that comprises a D.C. voltage source, an electric motor for cranking the engine, and a first switch that is selectively positionable to plural positions, one of which is a start position for cranking the engine.
A second switch is controlled by the first switch. A first input feed, comprising a circuit protection device, connects the D.C. voltage source to a first terminal of the second switch. A second input feed, that is free of any circuit protection device, connects the D.C. voltage source to a second terminal of the second switch. An output feed connects a third terminal of the second switch to an input terminal of a fourth switch that has an output terminal connected to the electric motor.
When the first switch is in any position other than the start position, the second switch connects the first input feed to the output feed, and when the first switch is in the start position, the second switch connects the second input feed to the output feed.
Another general aspect of the invention relates to a motor vehicle comprising an engine that is started by cranking and an electrical system that comprises a bank of one or more storage batteries, an electric motor for cranking the engine, and a first switch that is selectively positionable to plural positions, one of which is a start position for cranking the engine.
A second switch is controlled by the first switch. A first cable connects a terminal of the battery bank and a first input terminal of the second switch and is free of any circuit protection device. A second cable connects to an output terminal of the second switch for carrying current to the electric motor. A circuit protection device is in a current path from the battery bank terminal to a second input terminal of the second switch.
Placement of the first switch in any position other than the start position places the second switch in a first position that connects the second input terminal to the output terminal, and placement of the first switch in the start position places the second switch in a second position that connects the first input terminal to the output terminal.
Still another general aspect of the invention relates to a method for selectively protecting a cable that carries electric current from a bank of one or more storage batteries in a motor vehicle to an electric motor that cranks an engine in the vehicle when a first switch that is positionable to plural positions is positioned to a start position for starting the engine.
The method comprises when the first switch is placed in start position, causing a second switch to be placed in a position through which the second switch connects the cable to a terminal of the battery bank free of any circuit protection device, and when the first switch is placed in any position other than start position, causing the second switch to be placed in a position that connects the cable to the battery terminal through a circuit protection device.
A circuit protection device is understood to be any device that is intended to function by breaking a current path through itself when current through that path exceeds a rated current for which the device is designed.
The foregoing, along with further aspects, features, and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. The disclosure includes a drawing, briefly described as follows.